1. Field of the Invention
The present invention relates to linear gauges, and more particularly to construction of a linear gauge incorporating therein an optical reading device.
2. Description of the Prior Art
Heretofore, in the linear gauges of the type described, there has been adopted such a construction wherein a spindle provided at the forward end thereof with a measuring element is axially slidably supported by a frame, a glass scale is fixed on the inner end of the spindle and an optical reading device including a luminous element, a receptor element and the like is fixed on the frame. Further, as a spring for biasing the spindle in the extendedly projecting direction, there has been used a compression coil spring provided in the frame.
With the conventional construction as described above, the glass scale has been fixed on an extension of the spindle, whereby the movable portion becomes long and a stroke for the movable portion has to be provided upwardly of the glass scale, thus presenting a problem of that the frame is also increased in length.
Furthermore, use of the compression spring as the spring for biasing the movable portion has resulted in fluctuating biasing force in proportion as the spindle is changed in its position, thereby presenting a problem of that the measuring pressure fluctuates to a considerable extent.